This study was conducted to assess the effect of nettle supplementation on heat-stressed broiler performance and physiology. A total of 540 Ross-308 broiler chicks were randomly assigned to nine treatments each with six replications of 10 birds. Three contents of nettle were offered in either a fermented or unfermented (0, 1.5, and 3 g/kg) diet or in the drinking water (0, 1.5, and 3 g/L). At day 10, feed intake and FCR increased with nettle content in the diet. Heat-stressed birds that received powdered nettle had a better FCR. At day 35, increasing nettle improved the FCR. Nettle-supplemented broilers had increased dry matter, protein, and fat digestibility. The interaction of factors indicated that a higher NDV titre in birds that received 3% nettle in all forms. A higher NDV titre was found in birds that received fermented nettle, whereas a lower titre was found given the nettle extract. Unfermented nettle substantially increased the immunoglobulin titre of heat-stressed broilers. The interaction of factors indicated an increased total antioxidant capacity (TAC) in birds that received 3% of either fermented or unfermented nettle. The TAC was higher with fermented nettle. The activity of glutathione peroxidase increased with fermented nettle supplementation. Villi length and villous height/crypt depth increased with the supplementation of nettle and was higher in birds that received the unfermented nettle. In addition to its growth promoting properties, this study indicates nettle as a potential agent against heat stress in broiler production.